Fix tsc sourcemaps metadata

[mischnic]

"Closes" #7570, #7655
Closes #7876

1. In sources, tsc would only list the filename, not the relative path (like everything else in Parcel). So e.g. index.ts instead of packages/foo/src/index.ts. This also caused some duplicated entries because the JS transformer correctly used the complete path. Setting the mapRoot fixes this
2. The sourcecontent was missing for tsc. Apparently this is an unfortunate difference between return [{content, map}] and asset.setMap(); return [asset]; where the latter uses this code to automatically apply the sourcecontent
   

   parcel/packages/core/core/src/UncommittedAsset.js

   Lines 274 to 289 in 90a886f

   	setMap(map: ?SourceMap): void {
   	// If we have sourceContent available, it means this asset is source code without
   	// a previous source map. Ensure that the map set by the transformer has the original
   	// source content available.
   	if (map != null && this.sourceContent != null) {
   	map.setSourceContent(
   	fromProjectPath(this.options.projectRoot, this.value.filePath),
   	// $FlowFixMe
   	this.sourceContent,
   	);
   	this.sourceContent = null;
   	}
   	this.map = map;
   	this.mapBuffer = this.map?.toBuffer();
   	}

   
   (Furthermore, it now calls map.extends just like the JS transformer does)

[parcel-benchmark]

Benchmark Results

Kitchen Sink ✅

Timings

Description	Time	Difference
Cold	1.39s	-23.00ms
Cached	319.00ms	-22.00ms 🚀

Cold Bundles

No bundle changes detected.

Cached Bundles

Bundle	Size	Difference	Time	Difference
dist/legacy/parcel.7cdb0fad.webp	102.94kb	+0.00b	80.00ms	-4.00ms

React HackerNews ✅

Timings

Description	Time	Difference
Cold	9.03s	+101.00ms
Cached	417.00ms	+12.00ms

Cold Bundles

No bundle changes detected.

Cached Bundles

No bundle changes detected.

AtlasKit Editor ✅

Timings

Description	Time	Difference
Cold	1.47m	-447.00ms
Cached	1.98s	+1.00ms

Cold Bundles

No bundle changes detected.

Cached Bundles

No bundle changes detected.

Three.js ✅

Timings

Description	Time	Difference
Cold	6.56s	+13.00ms
Cached	255.00ms	+4.00ms

Cold Bundles

No bundle changes detected.

Cached Bundles

No bundle changes detected.

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